Field of the Invention
The present invention relates to a brake system comprising an electric braking force generator that brakes a wheel by using a driving force of an electric motor.
Description of the Related Art
Japanese Patent Application Laid-open No. 2005-343366 discloses a brake system of the type referred to as a brake by wire (BBW) brake system, which converts a braking operation of a driver into an electrical signal used to operate a motor cylinder or slave cylinder as an electric braking force generator, and operates a wheel cylinder by brake fluid pressure generated by the motor cylinder.
In an emergency situation such as collision avoidance, the rotational speed of the electric motor of the slave cylinder is required to be increased so as to quickly build-up the brake fluid pressure. However, if the rated rotational speed of the electric motor is set at a high value in order to enhance the response of braking force generation in an emergency situation, the rated torque decreases correspondingly, leading to a possibility that the torque of the electric motor becomes insufficient under normal operating conditions. If both the rated rotational speed and the rated torque of the electric motor are set at high values against this possibility, a problem occurs in that the size and/or price of the electric motor are increased.